Technical Field
This disclosure relates to systems and methods for adjusting the position and orientation of an end effector of a multi-axis machine, such as a manipulable cutting head of a fluid jet cutting machine.
Description of the Related Art
High-pressure fluid jets, including high-pressure abrasive waterjets, are used to cut a wide variety of materials in many different industries. Systems for generating high-pressure abrasive waterjets are currently available, such as, for example, the Mach 4™ five-axis abrasive waterjet system manufactured by Flow International Corporation, the assignee of the present invention, as well as other systems that include a cutting head assembly mounted to an articulated robotic arm. Other examples of abrasive fluid jet cutting systems are shown and described in Flow's U.S. Pat. No. 5,643,058, which is incorporated herein by reference. The terms “high-pressure fluid jet” and “jet” should be understood to incorporate all types of high-pressure fluid jets, including but not limited to, high-pressure waterjets and high-pressure abrasive waterjets. In such systems, high-pressure fluid, typically water, flows through an orifice of an orifice unit in a cutting head to form a high-pressure jet, into which abrasive particles may be combined as the jet flows through a mixing chamber and a mixing tube to form a high-pressure abrasive waterjet. The high-pressure abrasive waterjet is typically discharged from the mixing tube and directed toward a workpiece to cut the workpiece along a designated path.
Various systems are currently available to move a high-pressure fluid jet along a designated path. Such systems may commonly be referred to, for example, as three-axis and five-axis machines. Conventional three-axis machines mount the cutting head assembly in such a way that it can move along an x-y plane and perpendicularly thereto along a z-axis, namely toward and away from the workpiece. In this manner, the high-pressure fluid jet generated by the cutting head assembly is moved along the designated path in an x-y plane, and is raised and lowered relative to the workpiece, as may be desired. Conventional five-axis machines work in a similar manner but provide for movement about two additional non-parallel rotary axes. Other systems may include a cutting head assembly mounted to an articulated robotic arm, such as, for example, a six-axis robotic arm which articulates about six separate rotary axes.
Computer-aided manufacturing (CAM) processes may be used to drive or control such conventional machines along a designated path, such as by enabling two-dimensional or three-dimensional models of workpieces generated using computer-aided design (i.e., CAD models) to be used to generate code to drive the machines. For example, a CAD model may be used to generate instructions to drive the appropriate controls and motors of the machine to manipulate the machine about its translational and/or rotary axes to cut or process a workpiece as reflected in the model.
Manipulating a fluid jet about five or six axes may be particularly useful for a variety of reasons, for example, to cut a three-dimensional shape. To facilitate accurate machining of complex parts using a five-axis or six-axis machine it may be advantageous to adjust for any differences between the spatial location of a tool of the machine and an expected tool location defined by the design of the machine, which may arise from tolerance stackup, for example. The expected tool location may be dependent on a number of factors, including machine configuration. For example, in a five-axis fluid jet cutting machine having three translational axes and two non-parallel rotary axes that converge to form a machine focal point, the expected tool location may be located in line with or a selected offset distance from the machine focal point. In other machines, an expected tool location may be positioned relative to a reference frame of a terminal component or link of the machine.
In some instances, it is beneficial to align a tool of a machine with the machine's focal point. To set up or test whether a tool of the machine is aligned with the focal point or within a generally accepted tolerance range, it is known to perform manual measurements and physically adjust the alignment of the system based on such measurements, for example, by adjusting the position of the tool along various slide rails or adjustment slots that may be provided in tool mounting structures provided between the tool and the positioning system. Such adjustment systems, however, can be overly complex and bulky, which can result in increased costs and possible degradation of dynamic performance of the machine. Other systems for compensating for tool misalignment include assessing the magnitude and direction of the misalignment and compensating for them by making changes in the software (CNC code) that drives the machine motion.